In various types of self-propelled vehicles, such as service vehicles having traction motor apparatus, it is necessary to provide velocity control arrangements for adjusting the speed and direction thereof. Several schemes exist in the prior art which utilize hand-operated control mechanisms mounted on tiller structures coupled electrically and mechanically to the vehicle housing for providing both steering and motion control. However, each of these schemes suffers from limitations not found in the present invention. Many of the prior art control mechanisms provide for unidirectional or bidirectional constant speed motion while others provide for variable speed selection in either one or two directions.
One such exemplary arrangement is disclosed in U.S. Pat. No. 4,113,042, R. E. Vaill, issued Sept. 12, 1978, involving an electrically powered utility vehicle manually controlled by means of a speed selection switch mounted on the handle of the utility vehicle. Rotation of the speed selection switch by a craftperson generates a voltage control signal which is a function of the displacement of the rotation of the switch. A traction motor mounted within the utility vehicle is responsive to the voltage control signal for operating at a speed proportional to the level of the control signal. The rotational speed selection switch comprises a potentiometer having an adjustable resistance whereby the aforementioned voltage control signal is "picked off" of the potentiometer. However, speed control by means of potentiometer apparatus is sluggish in response to positional changes of the rotational switch and provides limited adjustment for loading conditions on the vehicle and traction motor.
A further prior art disclosure is U.S. Pat. No. 3,896,892, J. P. Kohls et al, issued July 29, 1975, wherein a self-propelled vehicle comprises an extendable tiller having a hand grip rotationally operable to regulate speed of the vehicle drive motor. Movement of the hand grip actuates movement of a magnet which controls reed switches for varying the energy applied to the motor of the self-propelled vehicle. Kohls is limited to discrete steps of speed control and requires a shunt relay control path for each discrete step designed therein.